Psoas abscess is a rare condition that might represent a diagnostic challenge. We report the case of a 47 years old male patient with diabetes mellitus and chronic pancreatitis, who was admitted for fever and severe pain of the left shoulder, in spite of a normal rheumatologic exam. The pain was interpreted as Kehr's sign when complementary investigations revealed a perisplenic collection, leading to the irritation of the diaphragm; the collection was extended to the left psoas muscle and resulted in psoas abscess. The psoas abscess represents a very rare complication of pancreatitis, favored in this case by the diabetic terrain. After the needle aspiration and percutaneous catheter drainage, along with antibiotics, the course was favorable. The case illustrates the importance of the referred pain and the clinical difficulties in the assessment of psoas abscess, manifested here only with fever and antalgic position. A brief review of the literature is then presented.